The weapon systems of attack aircraft have become more and more advanced, using weapons which are released from the aircraft at progressively further distances from the contemplated targets. As a result, the role of the air defense has gradually changed to one of combatting weapons that have been released from aircraft, for instance glide bombs, instead of combatting the actual aircraft itself. The ability of the air defenses to determine the position of an attacking aircraft or the position of the weapon released therefrom is based, to a large extent, on search radar and fire-control radar. The latter radar system initiates tracking of an attacking aircraft when the aircraft is far away. If the plane releases a so-called distance weapon at a point which is outside the range of the air defense artillery, it is essential that the radar is able to detect this occurrence and then shift target tracking to the actual weapon itself, so that the weapon can be shot down before it reaches its target.
It is difficult to detect the release of a weapon when the attacking aircraft is equipped with interference transmission equipment which disturbs the function of the radar. Transmission of noise within the radar frequency band is the most common form of interference, which renders the reflected pulses undetectable. This knocks-out the range finding ability of the radar. It is known to switch the radar to an angle tracking mode on the interference source in situations such as these, in which case the radar is used solely as a receiver. U.S. Pat. No. 4,136,343 describes a monopulse radio tracking system and a method a plurality of targets with the aid of a monopulse radar system installed on a target-tracking robot for the purpose of guiding the robot to a desired target, e.g. an aircraft. The radar is used as a receiver for signals which are transmitted from the ground and reflected by one or more enemy targets. The signals received are processed in a particular manner to establish whether the signals originate from one or from two targets located within the range covered by the radar antenna.